Considerable development has occurred with respect to electrically resistive elements, and particularly those suited for mounting in an electrical resistor device, such as a potentiometer, and adapted to be in engagement with a relatively movable contact member. Typically, a resistive element is affixed to some form of substrate is mounted within a potentiometer housing, and a rotatable or translatable contact member is in relatively movable engagement with the resistive element.
In recent years, a variety of materials and techniques have been developed for providing resistive coatings on a nonconductive substrate. In fact, certain conductive plastics have been employed to provide the resistance elements which are then mounted on a supporting substrate. Those conductive plastics typically incorporate carbon particles mixed within a thermosetting resin matrix to provide the conductive plastic resistance element. In some instances, that plastic resistance element may be of a fairly rigid form and in others, such as typified by U.S. Pat. No. 3,457,537, it may take the form of a flexible film which, in turn, is fixed in some manner to a rigid supporting structure.
Most typically, the conductive plastic resistance element is either directly connected to pre-deposited terminal elements or, as depicted in the aforementioned U.S. Pat. No. 3,457,537, employs rigid electrical contacts of a rivet shape which additionally serve to affix the resistive element to its respective substrate.
In those arrangements, the termination elements typically interrupt the otherwise smooth surface of the resistive element along which a movable wiper or contact travels. Because of the perturbations occasioned by such termination means, the wiper is either restricted in its movement beyond those points or may experience unwanted discontinuities in those regions and/or experiences excessive wear. Such interference between the wiper contact and the terminals associated with the resistance element have a similarly deleterious effect on the resistive element.
Certain processes and products associated with the field of electrical components and structures have given particular attention to arrangements for their termination. In one instance, typified by U.S. Pat. No. 4,554,732, provision is made for side-termination on discrete resistors comprised of a resistive film on a ceramic substrate. However, such resistors are not contemplated for use in engagement with a movable wiper contact.
Still further, U.S. Pat. No. 3,518,756 discloses a processes for fabricating a multi-level ceramic microelectronic structure in which various sheets are provided with via holes, electrode paste is deposited in those via holes and the sheets are then bonded together into a monolithic structure. Separate terminal holes will have been preformed in the several sheets such that upon final assembly, contact pins may be embedded in the terminal holes. However, that structure is rather complex in its assembly, it requires the insertion of rigid conductor pins and in any event is not intended for use in a potentiometric sense in which a movable contact or wiper is in engagement therewith.
Accordingly, it is a principal object of the invention to provide an improved method for making an electrically resistive element for mounting in an electrical resistor device and being of the type adapted for engagement with a relatively movable contact member. Included within this object are the provision of such an electrically resistive element and the method for its manufacture which result in an electrical resistor device product having high precision and relatively long life.
A further object of the invention is the provision of a method of making an electrically resistive element and the terminations therefor in such manner as to present little or no mechanical interference with a contact member moving in proximity therewith.
It is a still further object of the invention to provide a novel electrically resistive element manufactured in accordance with the method of the invention.